Analysis of forces and temperatures in friction spot stir welding of thermoplastic polymers

The present investigation analyses the force and torque developing during friction stir spot welding (FSSW) of thermoplastic sheets varying the main process parameters. In addition, measurements of the tool temperature and those of the material close to the welding region were carried out to better understand the variation of the forces during FSSW and quality of the joints. Experimental tests involving an instrumented drilling machine were performed on polycarbonate sheets. The study involved the variation of dwell time, tool plunge rate and rotational speed. Mechanical characterization and dimensional analysis of the joints were performed in order to assess the influence of the process parameters on the joint quality under considered processing conditions. According to the achieved results, using low values of the plunging speed has beneficial effects on both the process (reduction in the force and torque) and the mechanical behaviour of the joints. Increasing the tool rotational speed results in reduced processing forces and higher material mixing and temperature. The dwell time has a negligible effect on developing forces while it highly influences the material temperature, dimension of the welded region and consequently the mechanical behaviour of the joint.